Enthalpy measurement and evaluation of heat capacity on PuO

Morimoto, Kyoichi ; Ogasawara, Masahiro*

The heat capacity of MOX fuel is one of the important thermophysical properties. To evaluate the heat capacity of MOX fuel, the heat capacity of PuO is required because the heat capacity of MOX fuel is generally calculated from the compositional average of those of UO and PuO. The experimental results of the heat capacity of PuO are very scarce. In this study, the enthalpy of PuO pellet was measured in the temperature range from 980 to 2160 K with a drop calorimeter. In the measurement, the pellet was loaded in a tungsten container and a rhenium inner container was applied to prevent the reaction between the specimen and the tungsten container. It was found that the enthalpy increased at a constant rate with increasing temperature up to about 1900 K, and that above about 1900 K, its rate tended to increase with increasing temperature. It means that the heat capacity is raised when temperature exceeds about 1900 K.